1. Field of the Invention
This invention relates to alternative electrode supports and gas distributors for use in molten carbonate fuel cells which are designed to replace the expensive state-of-the-art electrode support components and allow for replacement of expensive ribbed separator plates currently in use in molten carbonate fuel cell stacks with inexpensive flat plates.
2. Description of Prior Art
Molten carbonate fuel cells have the potential for greatly decreasing the cost of generating electricity. In a typical application, a plurality of individual fuel cell units, separated by bi-polar electronically conductive separator plates, are stacked together and secured into a single stage unit to achieve a desired fuel cell energy output. Each individual cell generally includes an anode electrode, a cathode electrode, an electrolyte disposed between the anode electrode and the cathode electrode, and a fuel and oxidant gas source. Both fuel and oxidant gases are introduced through manifolds, either internal or external to the fuel cell stack, to the respective reactant regions thereof.
However, molten carbonate fuel cell stacks contain a variety of components that are inherently expensive in terms of both material and fabrication costs which greatly increase the overall cost of manufacturing molten carbonate fuel cell power plants and, therefore, the cost of electricity. One of the highest cost elements in a molten carbonate fuel cell stack is represented by the state-of-the-art perforated nickel plate used as an anode support and current collector. It is estimated that elimination of the anode support and current collector alone would significantly reduce material costs by $366 per kilowatt. Elimination of the state-of-the-art perforated stainless steel plate used as a cathode current collector would further reduce material costs.
In conventional molten carbonate fuel cell stacks, in addition to separating adjacent fuel cell units from one another, the separator plate is used to distribute reactant gases to the respective anode and cathode electrodes. To accomplish this distribution task, the separator plates are frequently patterned, such as by ribs or corrugations, so as to form channels through which the reactant gases flow for distribution to the respective electrodes. Such a separator plate is taught, for example, by U.S. Pat. No. 4,963,442 and U.S. Pat. No. 5,362,578. However, these stateof-the-art separator plates are also very expensive to produce.
One solution to these problems is the use of an electrode support in place of expensive and heavy state-of-the-art perforated nickel and stainless steel support plates/current collectors. U.S. Statutory Invention Registration H 16 to Kaun teaches a fuel cell having an anode, a gas impermeable matrix containing electrolyte, and a cathode. These three principal components are arranged in a stack and separated from adjacent fuel cells by gas impermeable electrically conductive separator plates. The electrodes comprise porous plaque support structures, each with an impregnated layer of catalyst material disposed in an inward, major surface section adjacent to the electrolyte matrix. The outward sections of the porous plaques are substantially free of catalysts, thereby enabling the admission and discharge of reactant gases.
It is also known to store a portion of the electrolyte required to operate a molten carbonate fuel cell in one or both of the electrodes whereby during initial heat-up/conditioning of the fuel cell, the electrolyte in the electrodes melts and flows into the electrolyte matrix disposed between the electrodes. However, it is desirable to use as thin electrodes as possible in a fuel cell to minimize the distances required for carbonate ions to travel during operation of the fuel cell. As a result, the electrodes are unable to store a sufficient amount of electrolyte to completely fill the electrolyte matrix.
Yet another problem with conventional fuel cell stacks is the shrinkage of the stack which occurs during initial heat-up resulting from the melting of carbonate tapes utilized to provide electrolyte to the electrolyte matrix. This is particularly problematic with larger fuel cell stacks. Accordingly, it is desired to provide a means for supplying electrolyte to the electrolyte matrix in a manner which overcomes the problems arising from shrinkage of the fuel cell stack during initial heat-up/conditioning.
Accordingly, it is one object of this invention to provide an electrode support for a molten carbonate fuel cell which eliminates the requirement of conventional fuel cell stack systems for expensive ribbed or corrugated separator plates.
It is another object of this invention to provide an electrode support for a molten carbonate fuel cell which provides the function of reactant gas distribution to the respective electrodes.
It is another object of this invention to provide an electrode support for a molten carbonate fuel cell which eliminates the highest cost elements in a molten carbonate fuel cell stack, namely the state-of-the-art perforated nickel plate used as an anode support and current collector and the state-of-the-art perforated stainless steel plate used as a cathode current collector.
It is yet another object of this invention to provide an electrode support for a molten carbonate fuel cell which is capable of supplying electrolyte to the electrolyte matrix of the fuel cell during initial heat-up/conditioning of the fuel cell.
These and other objects of this invention are achieved in a molten carbonate fuel cell comprising an anode electrode, a cathode electrode, and an electrolyte matrix disposed between the anode electrode and cathode electrode by an electrode support in accordance with one embodiment of this invention constructed of a high porosity reticulated foam material disposed on an electrode face (side) of the anode electrode and/or the cathode electrode facing away from the electrolyte matrix and forming a plurality of pores. An electrolyte is disposed within at least a portion of the plurality of pores, as a result of which at least a portion of the electrolyte flows into the electrolyte matrix during initial conditioning of the fuel cell.
The electrode support of this invention is an inexpensive, lightweight, and durable alternative to the current state-of-the-art expensive and heavy perforated nickel and stainless steel support plates/current collectors. Because the electrode supports of this invention are fabricated from highly porous, or very thin materials, they weigh only about 6% to about 25% of the weight of state-of-the-art anode and cathode current collectors. The electrode supports of this invention may be configured either as thin plates or as corrugated structures. We have found that regardless of which configuration is employed, the electrode supports of this invention are able to withstand the compressive forces encountered in a typical molten carbonate fuel cell. In addition, because each of the electrode supports also act as very low pressure drop gas distributors, it is possible to replace the expensive state-of-the-art ribbed separator plates with much cheaper, flat sheet metal plates, thereby substantially reducing overall fuel cell fabrication costs. The electrode supports of this invention are constructed in accordance with a particularly preferred embodiment of this invention from high porosity reticulated foam materials, and in accordance with other embodiments from corrugated supports made from thin perforated or expanded metal foils, and slotted metals.